Add Sourcery CodeBench Lite toolchain(s)

Sourcery CodeBench toolchains are prebuilt GCC toolchains from Mentor
Graphics.

Start out by adding ARM EABI and ARM GNU/Linux toolchains. Sourcery
CodeBench is also available for MIPS, Power, SuperH, ColdFire (and
more), so it should be easy to add later, if needed.

AFAIK, the EABI toolchains use newlib and the GNU/Linux ones use glibc.
Merge pull request #559 from bjornfor/mentor-codebench

Add Sourcery CodeBench Lite toolchain(s)